The use of arrayed molecules in formats such as microplates and biochips allows an ever increasing amount of information to be retrieved about the natural world. Although many variants are known, use of such arrays typically involves immobilizing probes or analytes on a substrate and using a variety of techniques to measure the interaction of the immobilized molecules with other, solution-phase, molecules. Specific examples of such array techniques include immunoassays (e.g., enzyme-linked immunoassays, ELISAs) that are performed in microplates, nucleic acid biochips (e.g., those commercialized by Affymetrix and Illumina) and protein biochips (e.g., the Invitrogen ProtoArray™). Biochips most commonly utilize glass substrates, while microplates for ELISA are often constructed from gamma-irradiated polystyrene. Although arrays are typically ordered, in the sense that immobilized molecules are placed at defined locations with respect to each other or to reference features, so-called “solution-phase arrays” have also been commercialized. The Luminex X-Map™ technology measures binding of analytes to a suspension of beads. The suspension is created by mixing batches of particles that are co-labeled with binding probes and corresponding mixtures of two fluorescent identifier molecules in varying ratios. Bound fluorescently labeled analyte is detected along with the identifier ratios using a flow cytometer.
In addition to the detection of individual molecules, particles (including biological cells) have been analyzed using array techniques. For example, it is known in the art to detect cell surface antigens through ELISA or flow cytometry. U.S. Pat. No. 6,251,615 to Oberhardt discloses testing cells using microscopy to detect cells bound to one of a plurality of capture zones with coupled antibody receptors.
A major limitation for conventional arrays is that long incubation times are usually required to reach a state of binding that is sufficiently close to equilibrium to allow useful analysis. This may entail allowing samples or reagents to incubate in an ELISA microplate or biochip for many hours, and in some cases, longer than a typical business day of 8 hours. Such delays can cause added expense, preclude use in emergency situations, and reduce data quality due to degradation of reagents during the protracted incubation times. Other limitations of conventional approaches is the need for analyte labeling steps and stringent washing steps, which introduce additional costs in terms of labor and equipment, and may impact data quality. Microplate based approaches use relatively large volumes of test samples and reagents.
As is known in the art, red blood cells (“RBCs”) from different patients may have different antigens on their surfaces, and transfusion of whole blood from a patient having certain RBC antigens to another patient that lacks those antigens may cause a deleterious immune reaction in the blood recipient. Therefore, blood typing is performed, typically by agglutination assay
Blood typing entails the identification of blood group antigens or antibodies as present on the surface of a subject's RBCs. Blood group A and B antigens are typically identified, as are various antigens associated with the Rh system, of which the D antigen is clinically the most critical. Currently, blood typing is performed by detecting the agglutination of red blood cells (RBC's) upon the addition of blood group antibodies (see, for example, U.S. Pat. No. 4,894,347 to Hillyard, et. al.). Agglutination of a blood sample indicates a positive result for an antigen matching the antibody added (for example, blood group antigen A, blood type antigen Rh).
Due to the variation in antibody reactivity from person to person, and due to possible prior existence of antibodies within a subject's blood, the potential exists for spurious results. A false result leads to incorrect blood typing, which can result, in turn, in the possibility of an adverse transfusion reaction. Moreover, current technologies require a relatively large amount of blood (˜3 mL) for testing. Therefore the ability to type blood while utilizing a smaller volume would increase donor comfort and be of great use when dealing with anemic patients such as newborns suffering from Hemolytic Disease of the Newborn (HDN). The ability to type blood from a single sample would also be a significant improvement over existing technology which currently used a blood sample that is separately inputted into multiple individual reaction volumes for every antigen tested.
Furthermore, the capacity to gauge the parallel interaction of small numbers of RBCs, or of other cells or more general organic bodies, with respect to a variety of reagents each having a known specific affinity for a particular analyte, would be of great analytical and diagnostic value. The parallel assaying of RBCs from a single blood sample with respect to antigens of both the ABO and Rh systems is an example of one application of such a system.
Holographic optical trapping (HOT) provides a useful tool for manipulation of microscopic and nanoscopic particles such as biological components. The basic principals of holographic optical trapping as well as systems configured to create and use such optical traps are disclosed in U.S. Pat. No. 6,055,106, U.S. patent application Ser. Nos. 10/701,324, and 09/886,802, the entirety of which are incorporated herein by reference.
In examining small sample particles in a microscope-based system, it is necessary to place the sample in a fluidic cartridge, such as a microscope slide so that it can be held in alignment with the optics of the microscope system. Such a fluidic cartridge may also be known as a sample slide, sample chip or cover slip. Sample slides useful in holographic optical trapping techniques are disclosed in U.S. patent application Ser. No. 10/294,599, U.S. Patent Publication No. 20030119177, the entirety of which is incorporated herein by reference.